The invention relates to a measuring method for characterizing a semiconductor component and also to a measuring device for a semiconductor component.
For determining physical parameters and, in particular, loss mechanisms in semiconductor components, spatially resolving measuring methods are advantageous, because in this way defined physical parameters or loss mechanisms could be allocated to defined spatial sub-areas of the semiconductor component and thus, for example, spatial inhomogeneities in the production process of the semiconductor component could be detected and analyzed in a simple way.
These methods are used, in particular, for characterizing semiconductor components in the form of semiconductor solar cells or precursors of such solar cells in the development process, i.e., a semiconductor element that has at least one pn junction. Below, the term “solar cell” is used both for designating the completed solar cell and also for its precursors in the fabrication process, as long as this precursor already has a pn junction.
For the spatially resolved measurement of a solar cell, measuring devices are known that comprise an illumination device, measurement electronics, and a camera system or some other spatially resolving detection unit. By means of the illumination device, the solar cell is typically illuminated over its entire surface area from the front and/or rear side. The free charge-carrier pairs generated in this way are separated at the pn junction of the solar cell.
The measurement electronics are typically connected to the electrical contacts of the solar cell, so that, by means of the measurement electronics, the working point of the solar cell, i.e., the current or voltage values at the electrical contacts can be specified.
For the quantitative or qualitative analysis, measurements at different working points along the current/voltage characteristic line of the solar cell are performed, in particular, in order to be able to separate different position-dependent parameters of the solar cells from each other.
Typical working points are short-circuit conditions (no voltage drop between the electrical contacts of the solar cell), open-circuit voltage (no current flow between the electrical contacts of the solar cell), and the optimal working point at which the output from the drawn current and the applied voltage is at a maximum.
The operating point selected for a measurement on the current/voltage characteristic curve of the solar cell decisively determines that local properties can be measured. Thus, for example, at the optimal operating point, the current flow from the solar cell is dependent on the local series-resistance network. In contrast, in the case of open-circuit voltages, no external currents are flowing, but equalization currents flow in any case internally in the solar cell, especially for spatially inhomogeneous loss mechanisms. These internal, lateral currents are typically rather small compared with currents at the optimal operating point of the solar cell, so that, in the case of the open-circuit voltage, the influence on the spatially resolved measurement due to current, for example, of the series resistance network of the solar cell, is negligibly small. Therefore, with typical measuring methods, no conclusions on the series resistance network of the solar cell are possible through measurements of the open-circuit voltage of the solar cell.